Field
The present disclosure relates to a printed circuit board and a display device including the same, and more particularly, to a printed circuit board in which the efficiency in distributing and disposing lines can be increased and a display device including the same.
Description of the Related Art
In general, a “printed circuit board” refers to a substrate manufactured by forming a metal layer on a thin insulator substrate and removing a part of the metal layer to configure an electronic circuit. The printed circuit board has been used in various fields. For example, a printed circuit board connected to a display panel in a display device is used to supply signals for driving the display panel or signals for controlling an operation of the display panel.
FIG. 1 is a cross-sectional view illustrating a related art display device. FIG. 2 is a plane view illustrating one of the metal layers of a printed circuit board in accordance with FIG. 1. In FIGS. 1 and 2, a related art display device 10 comprises a display panel 20 including a color filter substrate 21 and a TFT substrate 22, a back light unit 30, and a printed circuit board 40 under the back light unit 30.
The TFT substrate 22 includes a thin film transistor (TFT) configured to control a plurality of pixels including pixel electrodes and ON/OFF of a driving voltage transferred to each of the plurality of pixels. In the color filter substrate 21, a color filter for realizing a color, a common electrode, and a liquid crystal layer are disposed. However, the present disclosure is not limited thereto. The common electrode may be disposed in the TFT substrate 22 rather than in the color filter substrate 21. Although not illustrated in FIG. 1, a liquid crystal layer is interposed between the color filter substrate 21 and the TFT substrate 22. Further, a polarizing plate may be further provided on the color filter substrate 21 and under the TFT substrate 22. Because the display panel 20 is not self-luminous, the back light unit 30 configured to supply light to the display panel 20 is provided under the display panel 20.
As shown in FIG. 1, the printed circuit board 40 includes a plurality of insulation layers 41 and a plurality of metal layers 42 each disposed between the insulation layers 41. In the printed circuit board 40, a through-hole 49 penetrating the plurality of insulation layers 41 and the plurality of metal layers 42 is formed. A fixing bolt 50 may be inserted into the through-hole 49. The fixing bolt 50 includes a head part having a wide cross-sectional area and a longitudinal part extended from the head part in a longitudinal direction. Further, a fixing nut 31, which can be combined with the fixing bolt 50, is inserted into the back light unit 30. The fixing bolt 50 passes through the through-hole 49 of the printed circuit board 40 and then is engaged with the fixing nut 31 of the back light unit 30. The printed circuit board 40 is fixed to the back light unit 30 as described above.
As shown in FIG. 2, the through-hole 49 through which the fixing bolt 50 is inserted is formed in the metal layers 42 of the printed circuit board 40. The through-hole 49 is formed with a larger diameter than that of the fixing bolt 50 to allow for any error in insertion position of the fixing bolt 50. Thus, the longitudinal part of the fixing bolt 50 is disposed to be spaced away from the plurality of insulation layers 41 and the plurality of metal layers 42 within the printed circuit board 40. That is, a space is present between the longitudinal part of the fixing bolt 50 and the through-hole 49. Further, the longitudinal part of the fixing bolt 50 is not in direct contact with the inside of the printed circuit board 40.
The fixing bolt 50 may connect the printed circuit board 40 to the ground through the head part. Specifically, the head part of the fixing bolt 50 is brought into contact with a via 45 of the printed circuit board 40 so that the fixing bolt 50 is electrically connected to the printed circuit board 40. Further, the fixing bolt 50 is engaged with the fixing nut 31 inserted into the back light unit 30 and, thus, electrically connected to the back light unit 30. Therefore, the printed circuit board 40 is electrically connected to the back light unit 30 and then grounded through the via 45, the head part of the fixing bolt 50, and the fixing nut 31.
A ground area between the fixing bolt 50 and the printed circuit board 40 corresponds to a contact area between the via 45 and the head part of the fixing bolt 50. Thus, the ground area may be very small. Further, because the through-hole 49 is formed in the metal layers 42, lines 42A may not be disposed around the through-hole 49, which causes loss and limitation on space. Further, the lines 42A formed by patterning the metal layer 42 cannot overlap the through-hole 49 formed in the metal layers 42 and thus need to be turned or bent several times to avoid the through-hole 49. In this case, signal characteristics of signals transferred through the lines 42A may be adversely affected. Particularly, signals transferred through the lines 42A may be transmitted in pairs to minimize effects caused by external noise. For example, the signals transmitted in pairs respectively have voltages with different polarities. A voltage difference between the lines 42A transmitted in pairs is transferred as a single signal. Thus, the lines 42A transmitted in pairs need to have the same length. However, because the lines are disposed to avoid the through-hole 49, there will be a difference in length between a pair of lines, thereby deteriorating signal characteristics.
Accordingly, based upon such problem recognition by present the inventor and to solve such problem, a printed circuit board in which the straightness of lines and the layout efficiency of the lines can be increased and a display device including the same are needed.